Caves

Caves are giant holes that run horizontally underground. Holes that plunge vertically are called potholes. The most spectacular caves, called caverns, are found in limestone. Acid rainwater trickles through cracks in the rock and wears away huge cavities.

The world's largest known single cave is the Sarawak Chamber in Gunung Mulu in Sarawak, Malaysia.

The deepest cave gallery yet found is the Pierre St Martin system, 800 m down in the French Pyrenees.

The longest cave system is the Mammoth Cave in Kentucky, USA, which is 560 km long.

Many caverns contain fantastic deposits called speleothems. They are made mainly from calcium carbonate deposited by water trickling through the cave. Stalactites are icicle-like speleothems that hang from cave ceilings. Stalagmites poke upwards from the floor.

The world's longest stalactite is 6.2 m long. It is in the Poll an Ionian in County Clare, Ireland.

The world's tallest column is the Flying Dragon Pillar in the Nine Dragons Cave, Guizhou, China.